The invention relates to an arrangement for the quantitative and qualitative analysis of particles in gases, especially of particles in the exhaust gas of internal combustion engines, comprising a vibrating system with at least one vibration sensor, preferably a piezoelectric resonator, which is provided with at least one active collecting surface for the particles to be analyzed, which, through at least one outlet opening, enter the measuring chamber containing the vibration sensor, a circuit for determining characteristic vibration parameters, as well as guide and transport arrangements for the gas to be analyzed; as well as a process for the quantitative and qualitative analysis of particles in gases, especially of particles in the exhaust gas of internal combustion engines, in which the particles are precipitated through at least one outlet opening onto at least one active collecting surface of at least one stationary vibration sensor, preferably a piezoelectric resonator, of a vibration system, and by the particle precipitation there is determined the change of characteristic vibration parameters.
The measuring of particle emissions which arise in the combustion process of organic material has been of great interest for many years. The influence on human health of particles that are present in the breathing air stands at present at the center of many scientific investigations. Since the particles can be conceived as the measure of an incomplete combustion process, it is possible to raise the efficiency only by a continuous optimization of the combustion process and therewith to reduce the particle emission. From this continuous optimization there results high demands on the particle measuring system with regard to resolution, measuring range and dynamics. With vibration sensors, such as piezoelectric resonators for example, it is possible to determine the foreign mass applied directly to the sensor surface by means of the thereby occurring frequency change. In order to be able to measure the particle mass and/or the concentration of particles, with the aid of a probe, a certain volume of air is drawn through a particle collector. This measurement can be executed in one stage, so that if possible all the particles in the air stream are precipitated on a resonator, or in several stages, in which case here advantageously particles in defined size classes are precipitated on several resonators, wherewith not only the mass is determinable, but also a classification according to particle size is possible. The precipitation can occur, for example, by electrostatic processes, i.e., acceleration of the particles in the electric field onto the oscillating crystal, as is described, in U.S. Pat. No. 5,892,141.
The precipitation characteristic on the resonator collecting surface is given, in the case of gas samples fed-in through an opening, such as a nozzle or the like, directly over the resonator surface (an example for this is given in document U.S. Pat. No. 3,561,253), in addition to the flow-through, by the particle size, the geometry of the opening and its distance from the surface of the resonator. Even with several openings per resonator surface, as is disclosed in U.S. Pat. No. 4,446,720, after an initially linear decrease of the frequency, with rising particle load of the resonator, the frequency change above about 100 Hz begins to follow an exponential course.
In the article xe2x80x9cApplications of Piezoelectric Quartz Crystal Microbalancesxe2x80x9d in xe2x80x9cMethods and Phenomena, Their Applications in Science and Technologyxe2x80x9d, vol. 7, Elsevier 1984, an arrangement is described in which the vibration crystal is moved horizontally under a precipitation nozzle by means of a motor, in order to achieve a more uniform distribution of the particles. In such an arrangement, a relatively long period of time of several seconds is required until several layers of particles are precipitated, or the vibrating crystal must be moved back and forth very rapidly, for which purpose the arrangement must be built very stable and massive, and therewith correspondingly complicated and ill-suited for mobile use.
Also, from further documents on the state of the art, such as U.S. Pat. No. 5,056,355, no guiding arrangement for the gas stream is to be derived with which a control of the gas stream and therewith also of the particle stream would be possible to implement.
Likewise with the gas detector of DE 31 06 385, no arrangement is present which makes possible such a control of the impact zone of the particles over the collecting surface of the vibration sensor. On the contrary, it is a matter in this reference of a passive deflecting arrangement which does, to be sure, deflect the gas stream so that the latter will definitely pass onto the vibration sensor, but which then, however, permits no further influencing or control of the gas stream.
The problem of the present invention, therefore, is an arrangement and a process for the analysis of particles in gases, which with avoidance of the disadvantages of the state of the art, offers with a very simple and easy construction, as great as possible a measuring zone with a linear characteristic curve and therewith a great sensitivity and dynamics with respect to the mass loading in the entire measuring zone.
For the solution of this problem, the inventive arrangement described at the outset is characterized in that there are provided vibration sensors stationary with respect to the measuring chamber, and at least one active guiding and steering device for the gas or the particles contained therein. Therewith, despite a simple and easy construction, there can be achieved a uniform distribution of the precipitated particles over the active collecting surface of the vibration sensor, and therewith the desired wide measuring range with a linear characteristic curve and a high sensitivity and dynamics. Through the movement of the impact zone of the particles over the active collecting surface of the vibration sensor, the linear range of the frequency change by particle load can be significantly extended, since the saturation of individual zones can be avoided or at least be drawn out much longer than with conventional systems.
A first, structurally very simple and dependable form of execution of the arrangement according to the invention is characterized in that as an active guiding and controlling device there is provided a shutter with at least one shutter opening, the transversable cross section area of which is small as compared to the active collecting surface of the vibration sensor, in combination with an arrangement that moves the shutter relative to the active collecting surface of the vibration sensor, in which arrangement the movement runs essentially parallel to the active collecting surface of the vibration sensor.
According to a further feature of the invention, an arrangement is provided for the movement of the shutter, which moves at least one shutter opening on a closed path. Therewith, with as little as possible structure height, there can be achieved a uniform precipitation over a large surface area of the active vibration sensor surface.
In order to obtain s simple built arrangement, which is also attuned to the typically circular active collecting surfaces of the vibration sensors, there is provided an arrangement for the movement of the shutter, which moves at least one of the shutter openings over an essentially circular path, in which the axis of the circular movement is normally oriented essentially perpendicular to the active collecting surface.
Altogether it is provided there that the vibration sensor, and/or its active collecting surface, is advantageously constructed rotationally symmetrical about the axis of the circular movement, whereby there is achieved an optimal utilization of the collecting surface.
If, according to a further feature of the invention, an arrangement for moving the shutter is provided, which moves at least one shutter opening along a path that arises through the superposing of at least two rotary movements with essentially parallel axes of rotation, which axes of rotation are oriented essentially perpendicular to the active collecting surface, there can be achieved a still better and also more uniform surface coverage for the precipitation onto the active collecting surface of the vibration sensor, and that in a relatively short time.
According to a further feature of the invention, it is provided that an arrangement for the movement of the shutter relative to the vibration sensor is provided with an alternating speed, or with an alternating angular velocity.
For devices with electrostatic precipitation, the corona needle, present in any case, can be coupled according to the invention with arrangements for its movement relative to the vibration sensor, so that by reason of these movements, the electric field is continuously varied, and in this manner brings about the desired alteration of the impact zone of the particles on the vibration sensor. In this form of execution, additional components for the deflection of the gas jet or of the particles are avoided insofar as possible, whereby a light arrangement results, with which also the susceptibility to malfunctioning and the maintenance expenditure are again reduced.
According to a further form of execution of the invention, the arrangement can also be characterized in that as an active guiding and steering device, there is provided at least one arrangement for the generation of a variable electrical magnetic or electromagnetic field between the outlet opening and the vibration sensor, as well as an arrangement for the electrical charging of the particles in the gas. In order to obtain a defined deflection or altogether a deflection of the particles also for normally neutral particles, the particles should be electrically charged before reaching the outlet opening. This charge can occur mono-polarly or bi-polarly by a corona discharge or a radioactive source. With this form of execution, movable parts can be avoided to the greatest possible extent and therewith the weight of the apparatus, the susceptibility to malfunctioning, and the expenditure for its maintenance, can be significantly reduced. Further, in a simple manner and without complicated mechanical intervention, the path of the particle beam can be altered or adapted.
According to a further form of execution of the invention there is provided as an active guide and steering device, at least one outlet opening for an additional gas jet, preferably to the side of the opening for the entry of the particles, in which case the axes of the outlet openings preferably enclose between them an angle not equal to zero, or there can also be provided an active guide and steering device for the generation of an alternating current speed and/or direction. A further form of execution is presented by an arrangement in which the devices for the generation of alternating gas or of particle speeds are provided in the entry opening.
The process for particle analysis in gases described at the outset is characterized, according to the invention, in that during the measuring period, the particle jet is moved actively over an ever-alternating zone of the collecting surface of the vibration sensor. Thereby, a local saturation of the active collecting surface of the vibration sensor is avoided, the particles are distributed more uniformly on the active collecting surface and from this there results a substantial widening of the linear constituent of the measuring range, with higher sensitivity and dynamics with respect to the mass load over the entire measuring range.
Advantageously there, according to a further feature of the invention, it is provided that the particle jet is led along a closed curve, whereby a very uniform precipitation over a large surface area of the active collecting surface of the vibration sensor can be achieved with as small as possible a construction height if, according to a further feature of the invention, over the time interval of the measurement, an ever-alternating zone of the active collecting surface of the vibration sensor is excepted from the shielding, which zone defines a closed curve.
An especially simple variant there, which also takes into consideration the typical form of the active collecting surfaces of the vibration sensors, is characterized in that the particle jet is led along a circular path.
According to another development of the inventive process, the particle jet is led along a curve which arises by the superposing of at least two rotary movements with axes of rotation perpendicular to the active collecting surfaces. With this development there can be achieved a still better and also more uniform surface coverage for the precipitation of the particles on the active collecting surface of the vibration sensor, and that in a relatively short time.
Advantageously it is provided in all these variants that the particle jet is guided with an alternating speed, or with an alternating annular velocity.
In a variant embodiment of the invention with electrostatic precipitation, the electric field used for ionization of the particles can be continuously altered, so that therewith there occurs a change of the impact zone of the particle jet on the active collecting surface of the vibration sensor.
According to a further form of execution of the inventive process, there is provided, additionally to or alternatively to the above-described features, that the particle jet is deflected by an alternating electrical, magnetic, or electromagnetic field and led over the active collecting surface of the vibration sensor.
According to a further feature of the invention, it can also be provided that a gas jet of alternating flow speed and/or direction is directed onto the particle jet, and that the latter is therewith deflected.